This application is directed to wireless communication networks. More specifically, various embodiments of the present invention are used in wireless regional area networks. In particular, a specific embodiment of the present invention is implemented in compliance with the IEEE 802.22 standard to sense and/or detect available wireless communication channels within the television broadcasting frequency range. For example, embodiments of the present invention use a correlation method to determine frequency band availability. It is to be understood that embodiments of the present invention has a broad range of applicability and may be implemented for use in various types of wireless networks.
Wireless communication is one of the most important innovations in the twentieth century. One of the most important objectives of wireless communications and even general “radio” systems is to provide flexibility for different environments and requirements/restrictions and higher spectral and power efficiency in transmission, especially with confined frequency resources.
To fully appreciate and exploit the advantages of wireless communication systems, various concepts have been adopted in designing communication systems. With the advent of communication technologies and rapid increase of processing power of computers, it is often desirable and sometimes even necessary to adopt new system concepts and standards so that more intelligent systems can be implemented. For example, smart radio, software defined radio (SDR), reconfigurable radio, and cognitive radio, are being developed.
One aspect that needs improvement is the efficiency of spectral usage for a given frequency resource, especially for wireless communication systems. As of today, an increasing number of communication systems use wireless channels. As a result, many frequency bands are occupied by and assigned to the rapidly increasing applications and services. As a growing number of bands become assigned and occupied, the number of available bands becomes fewer and fewer. In addition, for a given frequency band, it is often a prerequisite to use this frequency band more efficiently without interference with other users.
In light of the above, more spectrally efficient systems need to be designed and new system concepts/technologies should be devised. One approach which is considered in this invention is that the frequency bands which are already assigned to other users are utilized opportunistically when the incumbent users do not operate in the bands. For example, in a related application Ser. No. 11/680,609 discloses a system for utilizing available television frequency bands for a wide regional area network (WRAN).
As discussed in the related application, it is well known that on the average, only around 40 percent of the TV broadcast bands are utilized at one instant. That is, the rest of 60 percent of the TV bands at one instant can be used for other applications/services provided that the spectral usage by the new services/applications does not interfere with the incumbent user signals. One specific application is for wireless regional area networks, for which the IEEE802.22 Working Group is to currently standardizing.
Using television broadcasting frequency bands for wireless networking has a great potential. In the Unite States, a typical local television broadcast area in the uses approximately 7 high-power channels out of the 67 available high-power channels that are allocated and reserved for television broadcasting. This means there are many free channels that can be used for wireless communication networks. Recently, the House of Representatives and the Senate passed bills requiring television broadcasts to switch from analog to digital by early 2009. As a result, the 700-MHz band (channels 52 to 69) will be cleared of programming and moved to lower frequencies (channels 2 to 51). The 700-MHz band will be set aside for public-safety emergency transponders and for bidding by wireless networks.
To be able to determine what frequency bands are available for wireless communications, it is often necessary to sense incumbent signals. Over the past, various conventional techniques have been developed for sensing incumbent signals. For example, techniques such as matched filter detection and energy band detection, have been developed. Unfortunately, these conventional techniques are often inadequate, as explained below.
Therefore, it is desired to have an improved method and system for determining wireless channel availability.